Furnace



Oct. 4, 1932. F. A. FAHRENWALD FURNACOIE Filed June 28,. 1929 4Sheets-Sheet l N Fan/z czjzmwa i Oct. 4, 1932. FAHRENWALD v 7 1,880,954

. FURNACE Filed June 28. 1929 4 Sheets-Sheet 2 111 '11 IIIIIIIIIIIIII /11 11/0111 Qt. 4, 1932. F. A. FAHRENWALD 1,880,954

FURNAC E Filed June 28, 1929 4 Sheets-Sheet 3 F. A. FAHRENWALD 1,880,954

FURNACE Filed June 28, 1929 4 Sheets-Sheet 4 fizz/922W v 2752705 Q.ji/refzzaali'.

Patented Oct. 4, 1932 FRANK A. FAHRENWA LD, OF CHICAGO, ILLINOIS FURNACEApplication filed June 28,

- My invention relates to high temperature equipment, and morespecifically to the continuous conveyor equipment employed for the heattreatment of metals at temperatures C such that ordinary steel and castiron are useless on account of insufficient mechanical strength orchemical reaction with other materials, or both. However, I am awarethat this type of equipment is suitable for the heating of materialsother than metals, such as ceramic articles. It includes among itsobjects and advantages a decrease in maintenance and operating cost, andan increase in speed and reliability in equipment of this 1- ype Onewidely used and most successful furnace of the continuous type is thatdescribed in my Patent 1,623,469. However, the rollers of such a furnacecannot handle small articles, such as bolts, nuts, forgings, andcylindrical pieces of rods, tubes, or bars, which must all have acontinuous supporting surface to carry them through the furnace.

One particular construction of continuous I conveyor now in use for thiswork employs one or more strands of chain operating over sprocketsoutside the ends of the hot chamber, with the load-carrying reach of thestrand sliding upon the hearth or in channels laid through the chamber.Such procedure has several drawbacks, including:

1) Excessive heat losses by carrying the hot conveying strand out of thechamber to the cold exterior;

(2) Slower production for a given size furnace, because the conveyingstrand as well as the material. has to be heated up;

(3) Excessive power required to drag the loaded strand across the hearthbecause the coefficient of sliding friction becomes very large at hightemperatures;

(4) Excessive abrasion and rapid wearing out of the conveyor strand, dueto heavy friction at high temperatures;

(5) Excessive tensile stress localized in the conveyor strand where itleaves the hearth;

(6) Rapid deterioration and disintegration of the strand parts byrepeated contraction and expansion due to temperature fluctuation;

1929. Serial No. 874,311.

, (7) Rapid wear on the supporting members over which the strand isdragged;

(8) Complicated furnace construction required to take care of the returnreach of such a strand; 1

In the accompanying drawings,

Figure 1 is a partly diagrammatic vertical central section through asmall unit according to the invention;

Figure 2 is a section. on line 2-2 of Figure 1;

Figure 3 is a diagram indicating the arrangement for supporting a longerconveyor strand;

Figure 4 is a similar diagram for a conveyor system of indefinitelength;

Figure 5 is a side elevation of the driving connections for such aconveyor system as that of Figure 4;

Figure 6 is a plan view indicating the arrangement of the sets ofconveyors in a conveyor system of indefinite length;

7 Figure 7 is a side elevation of a constant tension drive system; and

Figure 8 is a detail of a tension compensator.

In the embodiment of the invention selected for illustration in Figures1 and 2, the conveyor employs an endless flexible chain or strand ofheavy rugged construe tion, and passes over a supporting rotary sheaveor sprocket 10 at one end, and a similar member 12- at the other end,being supported on said members, with a catenary load carrying reach 14,and a oatenary return reach 16. The members 10 and 12 may be supportedon shafts 18 and 20 similar to those disclosed in my above mentionedpatent. which shafts extend out through the walls of the chamber 21 asclearly indicated in Figure 2. e

In such a system the only friction load inside the furnace is the slightflexing of the chain, or the movement of the chain parts into and out ofcontact with the teeth of the sprockets. On account of the hightemperatures and high friction coeflicients at such high temperatures,this flexing of the chain may constitute a substantial portion of thepower load. The gravity load is carried on the bearings outside, whichbearings operate at relatively low temperatures and can be designed forgood efficienc'y, so far as friction is concerned.

I have indicated the boundaries of the hot chamber at 22 in Figure 1,and a series of-billets, or pieces of material at 24 resting on thestrand and passing through the furnace in the direction of the arrow 26.

The bearings 28 for the shaft 20 are fixed and immovable, but thebearings for the shaft 18 are mounted on small' carriages 3O slidablelongitudinally of the conveyor and resiliently pulled away from thebearings 28 by suitable means, such as tension cords 32 passing overpulleys 34 and attached to weights Such'a mounting guarantees asubstantially uniform and constant tension for the conveyor strand. Whenthe strand is heavily loaded, the bearings for the shaft 18 will slideand permit the strand to sag a little more so as to carry the increasedload Without any increase in tension.

Referring now to Figure 3, I have indicated a conveyor strand 38, ofsomewhat greater length than can be safely supported in a singlecatenary span at the high temperatures prevailing. To reduce the tensionin the strand necessary. to carry the weight of the strand and its load,I may provide a central idler 40. In many in stances, especially at hightemperatures, the major portion of the mechanical load on the system istheweight of the strand, as the strand Weighs more per unit length thanthe load placed upon it. In such cases I provide a lower idler 42 forgiving the return reach of the strand the same support given the loadcarrying reach by the idler 40. These idlers 40 and 42 are of identicalconstruction with the shafts 20 and sprocket 12. I To make up a furnaceof indefinite, length without dragging the conveyor strand, I maycontinue the system of Figure 3 or I may employ the system of Figures 4and 6. I have indicated four transverse shafts 44, 46, 48 and 50. Theend shafts 44 and 50 each carry four rotary members, and theintermediate shafts 46 and 48 each carry eight rotary members.

Each span is bridged by four conveyor strands 52. the strands insuccessive spans being laterally offset enough to provide roomformounting the additional rotary members on the intermediate shafts.When such a series of shafts has outside bearings, the shafts may bedriven in unison by mounting worm wheels 54 on the ends of the shaftsand driving all the shafts from a line shaft 56 through worms 58 asshown in Figure In such an installation, the of each cateuary spandepends on the temperature at which the furnace is operating.

In such a drive, I prefer to provide all the shafts with longitudinallyadjustable bearings, so that the spacing of the shafts may be adjustedto let the conveyors sag the are supported by bearings slidablelongitudinally of the furnace. If the tension in each reach of eachstrand is T, the force between each pair of shafts tending to draw themtogether will be 8T.

\Veights 60 attached to the tensioning cords 62 for the shaft 44, eachequal to 4'1, will tension the entire system, as the longitudinal forcesacting on intermediate shafts 46 and 48 are balanced.

To turn the shafts Without interfering with the tensioning of thestrands, I drive the shaft 50 through a worm 64 and worm wheel 66, andrun a cold chain 68 over sprockets 70, 72, 74 and 76 on the shafts 50,48, 46 and 44, respectively. I may now apply a load or torque to eachshaft to turn it. These loads will be approximately but not exactlytwice as great for shafts 46 and 48 as for shafts 44 and 50, becausethereare twice as many strands being curled up and straightened outaround the shafts 46 and 48 as there are around the shafts 44 and 50.

Thus, I apply a tensioning weight 78 pulling on a bight 80 in the reachof the cold chain 68 between shafts 44 and 46. The amount of this weightI have designated as P and to hold the sprocket end of shaft 44 in placeit is accordingly necessary to add the same amount of weight at 60,making the total weight applied there 4T+P. Similarly I increase thetension by another tensioning weight 82 pulling on a bight 84 betweenshafts 72 and 74. Approximating the torque load of shaft 46 at twicethat on shaft 44, the weight 82 should weight ESP, and the sprocket endof shaft 46 will need to be held in place by a counter weight 86 equalto 2P. Between shafts 50 and 48 it will similarly be necessary to employa tensioning weight 88 equal to SP pulling on the bight 90, and tocounter-balance the sprocket end of shaft 48 with a counter weight 92equal to 2P.

It will be obvious that in practice these weights will be adjustedwhenthe furnace is first set up and that the 1: 3: 5 ratio enumerated ismerely an approximation, the weights in practice being adjusted to theamounts that will secure a proper balance.

To provide a slight change in tensioning in case of displacements I mayarrange the Sides of the bights 80, 84- and 90 to diverge slightly asindicated in Figure 7. When such an arrangement is employed, any slightshifting, lifting any one of the tension weights, will slightly increasethe tension developed by said weight and there will be a mild tendencyto come back to the equilibrium position. This reduces the sensitivityof the system to slight changes in load.

An alternative and much more adaptable variable tensioning means is thatillustrated in Figure 8. Any one of the tensioning or counter balancingweights of Figure 7, and

preferably all of them, may be made up of a top Weight 94 and aplurality of auxiliary weights 96 connected in series under the topWeight by clips 98, each pair of clips mounted on the weight above, andhaving toes 100 fitting loosely in sockets 102 in the weight below.Thus, every displacement of the shaft or sheave to which the weightisattached by the hook 104 will pick up an additional auxiliary weight,each time the displacement amounts to the play in one socket. In thisway the rate at which restoring forces are generated by any displacementmay be varied in any arbitrary way to suit the conditions of service.

In some installations where certain displacements might become critical,I may provide a support 106 in the form of a housing for .a springpressed electric switch 108 so that the lifting of the lowermost weight96 will complete a circuit through a wire 110, a source of electromotiveforce 112, and a bell or some equivalent alarm means 114.

lVithout further elaboration the foregoing will so fully explain thegist of my invention that others may, by applying knowledge current atthe time of application, readily adapt the same for use under variousconditions of service.

I claim:

1. Equipment for conveying materials at high temperatures comprislng achamber, an

' endless conveyor strand, the load carrying reach of said strand beinglocated in said chamber and suspended as a catenary span, rotatingmembers for supporting said span, said rotating members and the returnreach of said strand being located inside said chamber, shafts carryingsaid members, a power drive for rotating the shaft at the discharge endof the strand, and gravity actuated means acting on said other shaft formaintaining constant tension in said strand.

2. Equipment for conveying materials at high temperatures comprising achamber, an endless conveyor strand, the load carrying reach of saidstrand being located in said chamber and suspended as a catenary span,rotating members for supporting said span, said rotating members and thereturn reach of said strand being located inside said chamber, a powerdrive for moving said strand,

and means for maintaining constant tension in said strand.

3. Equipment for conveying materials at temperatures above 1400 Fcomprising a chamber, an endless conveyor strand, the load carryingreach of said strand being located in said chamber and suspended as acatenary span, rotating members forsupporting said span, said membersand the return reach of said strand being located inside said chamber,shafts carrying said members and extending transversely outside thefurnace, bearings outside the furnace for the ends of said shafts, apower drive for rotating the shaft at the discharge end of the strand,the bearings for the shaft at the other end being longitudinallyslidable, and gravity actuated means acting on said slidable bearingsfor maintaining constant tension in said strand.

4. Equipment for conveying materials at temperatures above 1400 F.,comprising a chamber, a plurality of sets of endless flexible conveyorstrands in said chamber, each set longitudinally offset from adjacentsets, the individual members of each set being laterally offset from theindividual members of adjacent sets, the adjacent ends of adjacent setsbeing looped around a common axis, a plurality of transverse shafts forsupporting said strands by catenary suspension, and power transmissionto turn all said shafts.

5. Equipment for conveying materials at high temperatures, comprising achamber, a plurality of sets of flexible endless con.- veyor strands insaid chamber, each set longitudinally offset from adjacent sets, theindividual members of each set being laterally offset from theindividual members of adjacent sets, the adjacent ends of adjacent setsbeing looped around a common axis, a plurality of transverse shafts forsupporting said conveyors by catenary suspension,- and powertransmission to turn all said shafts.

6. Equipment for conveying materials at high temperatures comprising achamber, flexible conveyor strand means in said chamber suspended in aplurality of catenary spans, supporting members at the ends of eachspan, transverse shafts carrying said supporting members, tension meansfor maintaining constant tension in all said spans, and means fortransmitting power to each shaft independent of the operation of saidtension maintaining means.

7. Equipment for conveying materials at high temperatures comprising achamber,

supporting members, tension means for maintaining constant tension inall said 8. Equipment for conveying materials at high temperaturescomprising a chamber,

' flexible conveyor strand means in said chamber suspended in aplurality of catenary spans, supporting members at the ends of eachspan, transverse shafts carrying said supporting members, a power driveacting on the ends of said shafts, and tension means for maintaining thetension in all said spans susbstantially equal and substantially constant.

9. Equipment for conveying materials at high temperatures comprising achamber, flexible conveyor strand means in'said cham-' ber suspended ina plurality of catenary spans, supporting members at the ends of eachspan, transverse shafts carrying said supporting members, sprockets onthe ends of said shafts outside the chamber, a cold chain passing overall said sprockets, and tensioning means in each load carrying reach ofsaid cold chain adjustable for maintaining a predetermined tension insaid reach.

10. High temperature conveying equipment comprising a catenary conveyorstrand, a weight, and connectlons between said .weight and strand forautomatically maintaining the tension in all parts of said strandsubstantially the same when loaded as when unloaded.

11. The combination with a chamber maintained at 1400 F. or more, of acatenary conveyor in said chamber, transverse supporting i f meansoperating by displacing said shafts toward and away from each other forvarying the sl'ackness of said catenary to compensate for variations inthe load thereon.

13. The combination with a chamber'maintainedat 1400 F. or more, of acatenary conveyor in said chamber, transverse upporting a shafts for theends of said conveyor,.said

shafts having ends extending, outside saidchamber, and means engagingthe ends of said shaft and operating by displacing said shafts towardand away from each other for automatically varying the slackness of saidcatenary as a function of the load. thereon.

14. Equipment for conveying materials at high temperatures comprising achamber, flexible conveyor strand means in'said chamber suspended in aplurality of catenary spans, supporting members at the ends of eachspan, transverse shafts carrying said supporting member's, sprockets onthe tained at high temperature, of a catenary conveyor in said chamber,transverse supporting shafts for the ends of said conveyor, and meansoperating by displacing said shafts toward and away from each other forautomatically varying the slackness of said catenary as a function ofthe load thereon.

Intestimony whereof I hereunto affix my signature.

FRANK A. FAHRENWALD.

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